1. Field of the Invention
The invention relates to a solid secondary battery system capable of recovering deterioration in output characteristics.
2. Description of Related Art
With the recent rapid spread of information-related equipment or communication equipment such as personal computers, video cameras and mobile phones, manufacturers and developers are placing more importance than ever on development of batteries used as power sources in such equipment. In automobile industries as well, development of high-output and high-capacity batteries for use in electric or hybrid vehicles has been pursued. Currently, among a variety of batteries, lithium secondary batteries are the ones attracting the most attention for their high energy density.
Lithium secondary batteries currently on market typically have electrolyte containing a combustible organic solvent. Therefore, they require provision of a safety device for suppressing increase in temperature in case of short circuit, or improvement in configuration or materials for preventing occurrence of short circuit. On the other hand, solid lithium secondary batteries are provided with a solid electrolyte layer in place of the liquid electrolyte so that they are made in solid state. Since no combustible organic solvent is used in such solid lithium secondary batteries, the safety devices can be simplified, and hence these solid lithium secondary batteries are considered to be superior in terms of manufacturing cost and productivity.
In addition, secondary batteries, which can be repeatedly charged and discharged, are apt to be deteriorated in battery performance by overdischarge. Therefore, conventional secondary batteries are provided with means for measuring a battery voltage during discharge and terminating discharge when the battery voltage reaches a predetermined value. On the other hand, Japanese Patent Application Publication No. 2010-225581 (JP-2010-225581 A) discloses a battery module which has no overdischarge protection means for preventing overdischarge of a lithium secondary battery. Japanese Patent Application Publication No. 2010-225582 (JP-2010-225582 A) discloses a dynamo-electric device having no overdischarge protection means for preventing overdischarge of a lithium secondary battery.
Solid secondary batteries in general have a problem that repeated charge and discharge cause increase of internal resistance and deterioration of output characteristics. The solid secondary batteries further have a problem that when stored at a high temperature (e.g. about 60° C.), internal resistance is increased and output characteristics is deteriorated. It is usually difficult to recover the output characteristics once deteriorated.